Ink tank, head cartridge and ink-jet printing apparatus

Abstract: A length (c) of a melamine foamed block (12) to be accommodated in an ink tank housing (11) as measured in the longitudinal direction is dimensioned to be larger than a length (C) of the ink tank housing (11) as measured in the longitudinal direction. Thus, while the foamed block (12) is accommodated in the ink tank housing (11), it is compressed in the direction orienting toward an ink feeding port (13) from which ink is fed to a printing head (14), i.e., in the ink feeding direction. Consequently, the ink retaining force induced by the capillary force is not intensified in the compressing direction of the melamine foamed block (12), resulting in an ink feeding capability of the printing head (14) being improved. On the contrary, the ink retaining force effective at a right angle relative to the compressing direction of the melamine foamed block (12) is intensified.

Description: The present invention relates to an ink tank according to claim 1, a head cartridge according to claim 3, and an ink jet printing apparatus according to claim 6. The documents EP-A 0 580 433 and EP-A 0577 439 constitute a prior art pursuant to Article 54(3)(4) EPC. From the EP-A 0 580 433 an ink-jet cartridge is known which includes a first chamber which accommodates a negative pressure producing material and an air communication part, as well as a second chamber which communicates with the first chamber. The second chamber directly accommodates the ink to be supplied to the first chamber. From the EP-A 0577 439 an ink tank is known which is filled with compressed fibre materials by which ink is transmitted therethrough by a capillary force. The bulk density of the fibre material in the region adjacent to the ink feed passage of the ink tank is greater than the bulk density of the fibre material in the region remote from the ink feed passage. Here, the printing operation represents all type of operations each to be performed for a various. kind of ink receiving medium such as a cloth, a thread, a paper, a sheet-like material or the like so as to allow ink to be adhesively secured thereto. Therefore, the present invention can be applied to a printing apparatus, i.e., a printer serving as an information outputting apparatus operatively associated with a various kind of information processing apparatus. Many foamed blocks each molded of a polyurethane resin are hitherto used as an ink absorbing member to be accommodated in an ink tank of the foregoing type. In the case that a urethane foamed block is used as an ink absorbing member, films are formed in the foamed block during each molding operation in such a manner as to wrap each of a number of voids (pores) in the foamed block with a film. Thus, since the voids are isolated from each other due to the presence of the film between adjacent voids, the foamed block can not exhibit a function of absorbing ink therein as it is. To cope with this problem, the foamed block is subjected to film removing treatment via heating, cleaning and others. However, it is very difficult to completely remove films in the foamed block with the film removing treatment as mentioned above. In most cases, a considerable amount of residue practically adheres to each void or pore on completion of the film removing treatment. In the case that the urethane foamed block is used as the ink absorbing member, it is usually accommodated in the ink tank in the compressed state. In addition, to assure that an adequate intensity of negative pressure acts on a communicating portion between the foamed block and a connecting member for an ink outflow portion while maintaining a certain pressure gradient across the foregoing communicating portion, a part of the foamed block is usually compressed at the communicating portion. However, since film residues remaining between adjacent voids or pores are liable to overlap in the foamed block, there arise malfunctions that ink hardly flows in the ink absorbing member, and moreover, ink fails to be fed outside of the ink tank. On the other hand, in contrast with the urethane foamed block, an ink absorbing member comprising a foamed block molded of a condensate composed of a melamine and a formaldehyde is described in an official gazette of, e.g., International Patent Laid-Open Publication NO. WO 91/02652. The ink absorbing member as described in the above official gazette is molded in the form of a skeleton having no thin film in each gap present in the circuit network of the foamed block while assuming a net-shaped structure. Thus, the ink absorbing member composed of a melamine foamed block has many advantages that any type of film removing treatment is not required, a large quantity of ink can storably be received in the melamine foamed block owing to the presence of a number of fine fibers constituting the circuit network compared with the urethane foamed block, initial ink filling treatment can easily be conducted owing to an excellent hydrophilic property of the melamine foamed block in contrast with the urethane foamed block having a water repelling property, no ink remains in the melamine foamed block having no film formed therein due to the presence of a residue on completion of ink consumption, and the ink in the melamine foamed block can completely be utilized at a high efficiency. Basically, it is preferable that the ink absorbing member composed of a melamine foamed block which is disclosed in the above-stated gazette is practically used in the compressed state, and ink is fed to an ink outflow portion disposed at the lower part of an ink tank by the function of the gravity force of ink itself. Thus, the ink feeding direction orienting toward the ink outflow portion is firmly determined to coincide with the downward direction. For this reason, there arises a problem that an attitude to be assumed at the time of practical use of the ink tank described in the official gazette is restrictively determined. In addition, in the case that the ink absorbing member is accommodated in the ink tank in the preferably employable uncompressed state, it is difficult that the ink absorbing member is brought in close contact with the inner wall surface of the ink tank. Thus, a gap is liable to appears between the ink absorbing member and the inner wall surface of the ink tank. When the atmospheric air taken through an atmospheric air communication port or an ink ejecting port of an ink jet head stays in the gap, there arises a malfunction that as ink is ejected from the ink jet head, a bubble is involved in the ink fed to the ink jet head, causing a quality of printed image to be remarkably degraded. Especially, with respect to an ink jet recording apparatus of the type including an ink tank and an ink jet head integrated with each other to perform a printing operation by reciprocably scanning the integrated structure composed of the ink tank and the ink jet head relative to a printing medium, there readily arises a problem that the ink tank is vibratively displaced due to the reciprocable scanning of the foregoing integrated structure. In the case that the ink jet printing apparatus is adversely affected by the vibrative displacement of the ink tank or in the case that the ink tank includes a member at the position located in the vicinity of an ink outflow portion, when a part of the ink absorbing member located in the vicinity of the ink outflow portion exhibits deterioration in terms of properties as time elapses, a gap is liable to appear at the above-noted part of the ink absorbing member. At this time, it is anticipated that the adverse influence given to the ink absorbing member due to staying of air at the gap becomes more remarkable. In an extreme case, it is preestimated that the atmospheric air communicating portion and the gap located in the vicinity of the ink outflow portion are communicated with each other. Once such a malfunction as mentioned above has arose, it becomes impossible to perform a desired ink ejecting operation, and moreover, the ink present in an ink feeding path leaks from an ink ejecting port, causing the interior of the ink jet printing apparatus to be contaminated with the leaked ink. Since feeding of ink to the ink outflow portion is achieved by utilizing the gravity force of the ink itself, when an ink jet head is driven at a high frequency highly desired in recent years, there is a possibility that the ink feeding can not follow the driving of the ink jet head at a high frequency. To improve a property of followability of the ink jet head at the driving of the latter at a high frequency, it is thinkable that a pore size is enlarged to some extent and a magnitude of resistance against flowing of the ink is reduced. In this case, however, there is a possibility that an ink retaining capability of the ink absorbing member is degraded, causing ink to leak from the atmospheric air communicating port. According to the description of the official gazette of the prior invention, in some case, it is desirable that a certain intensity of compressing force is applied to a foamed structure for the ink absorbing member in a specific application example of the ink jet printing apparatus in order to maintain useful or suitable properties of the ink absorbing member in the uncompressed state, and moreover, adjust a gap space of the foamed structure. It is considered that the description of the official gazette was made in consideration of the relationship between inner dimensions of the accommodating space and outer dimensions of the ink absorbing member. The inventors of the present invention conducted a variety of examinations and as a result derived from the examinations, they found that it was acceptable that the ink absorbing member was properly compressed in order to assure that ink could smoothly and reliably be fed to the ink absorbing member regardless of an attitude assumed by the ink tank while utilizing advantages of the ink absorbing member molded of a condensate composed of a melamine and a formaldehyde. In addition, the inventors found the following technical problems to be solved. Specifically, one of the problems is that the ink absorbing member should be compressed corresponding to the structure of the ink absorbing member in a certain adequate direction in order to assure that ink can smoothly be fed to the ink absorbing member, other one is that so-called warpage or breakage is liable to occur at a compressible part of the ink absorbing member having a comparative brittle fibrous structure, and another one is that once the warpage has occurred with the ink absorbing member, the compressed state of the latter can not be maintained any more, resulting in the ink absorbing member assuming an uncompressed state. In addition, a filter is usually disposed at the ink outflow portion for removing foreign materials involved in the ink fed from the ink absorbing member, and an opening area of the ink outflow portion is determined corresponding to a quantity of ink to be fed therefrom. However, since the thermosetting melamine based condensate is brittle in structure, a part of the condensate is peeled away from the ink outflow portion when the ink absorbing member is worked, accommodated in the ink tank or put in later practical use, and the filter is clogged with fractured pieces of the condensate. In this connection, the inventors found another technical problem to be solved at this time, i.e., a problem that a desired quantity of ink to be fed could not be assured with the ink absorbing member. These technical problems mentioned above is not described in the official gazette. The object of the invention is to provide an ink tank, a head cartridge, and an ink jet printing apparatus by which the ink feeding capability is improved. This object is achieved by the combinations of the features defined in the independent claims 1, 3, and 6. Preferred embodiments of the subject-matters of claims 1 and 3 are set forth the dependent claims. In the following, embodiments of the invention are described in detail with reference to the accompanying figures. Fig. 1 is a partially exploded schematic perspective view of an ink tank constructed according to an embodiment of the present invention, showing the structure of the ink tank; Fig. 2A and Fig. 2B are sectional views which show by way of two examples of the structure of the ink tank shown in Fig. 1, respectively; Fig. 3 is a schematic sectional view of a head cartridge for which the ink tank shown in Fig. 1 is used; Fig. 4 is a schematic sectional view of the ink tank constructed according to the embodiment of the present invention, showing an initial state of the ink tank; Fig. 5 is a schematic sectional view of the ink tank constructed according to the embodiment of the present invention, showing an intermediate state of usage of the ink tank; Fig. 6 is a schematic sectional view of an ink tank constructed according to an embodiment modified from the embodiment of the present invention; Fig. 7 is a graph which shows how an inner pressure in the ink tank constructed according to the embodiment of the present invention; Fig. 8 is an illustrative view of the ink tank constructed according to the embodiment of the present invention, illustratively showing how a compressible absorbing member in the ink tank functions as a buffer type absorbing member; Fig. 9 is a graph which shows the relationship between a volume of initial hollow space of the ink tank constructed according to the embodiment of the present invention and a quantity of ink flowing outside of the hollow space of the ink tank when an inner pressure in the ink tank is reduced; Fig. 10 is a schematic sectional view of the ink tank constructed according to a comparative example, showing how ink leaks from the ink tank; Fig. 11 is a schematic sectional view of the ink tank constructed according to a comparative example, showing how ink leaks from the ink tank; Fig. 12 is a schematic sectional view of the ink tank constructed according to a comparative example, showing how ink leaks from the ink tank; Fig. 13 is a schematic sectional view of the ink tank constructed according to the embodiment of the present invention, showing how ink flows in the ink tank when an atmospheric pressure in the ink tank is reduced; Fig. 14 is a schematic sectional view of an ink tank constructed according to an embodiment modified from the embodiment of the present invention; Fig. 15 is a schematic sectional view of an ink tank constructed according to another embodiment modified from the embodiment of the present invention; Fig. 16 is a schematic sectional view of a head cartridge for which an ink tank constructed according to a modified embodiment of the present invention is used, showing an initial state of the head cartridge; Fig. 17 is a schematic sectional view of the head cartridge shown in Fig. 16, showing an intermediate state of usage of the head cartridge; Fig. 18 is a schematic fragmentary enlarged sectional view of the head cartridge constructed according to the modified embodiment of the present invention, illustratively explaining a principle of ink feeding and generation of an inner pressure in the ink tank; Fig. 19 is a graph which shows how an inner pressure of ink in an ink feeding portion of the head cartridge constructed according to the modified embodiment of the present invention varies; Fig. 20 is a schematic sectional view of a head cartridge constructed according to another embodiment modified from the embodiment of the present invention, showing how a buffer type absorbing member in the ink tank functions; and Fig. 21 is a perspective view of an ink jet printing apparatus adapted to perform a printing operation using the head cartridge constructed according to the embodiments as mentioned above. The following embodiment is intended to use an ink absorbing foamed block molded of a melamine resin for ink tanks each having a various kind of structure. Fig. 1 is a partially exploded schematic perspective view of an ink tank constructed according to the embodiment of the present invention, and Fig. 2A is a schematic sectional view of the ink tank shown in Fig. 1. In this embodiment, as shown in the drawings, the interior of a housing 501a of an ink tank 501 is divided into two ink chambers a and b with an ink chamber wall 501b interposed therebetween, and both the ink chambers a and b are communicated with each other via an aperture formed on the bottom of the ink tank 501. An ink absorbing member F, of which capillary force is properly adjusted, is accommodated in the ink chamber a . An ink feeding portion 502 and an atmosphere communicating portion 503 are formed through the right-hand side wall of the ink chamber a for connecting the ink tank 501 to an ink jet head (not shown). The positions assumed by the atmosphere communicating portion 503 and the ink feeding portion 502 should not be limited only to the shown ones. Alternatively, they may be formed through the housing 501a of the ink tank 501 in the positional relationship as shown in Fig. 2B. Fig. 3 is a schematic sectional view of a head cartridge for which the ink tank shown in Fig. 1 is used, particularly showing the state that an ink jet head, and ink tank and a carriage constituting an ink jet apparatus are connected to each other. In this embodiment, a bubble jet process is employed for an ink jet head 510 which serves to achieve a recording operation using an electrothermal converting element for generating thermal energy required for inducing a phenomenon of film boiling in ink in response to an electric signal. All essential components constituting the ink jet head 510 are arranged on a head base plate 511 one above another by adhering or crimping in the laminated state while a position determining protuberance formed on the head base plate 511 is taken as a position determining datum. The position of the ink jet head 510 on the paper plane of Fig. 3 as seen in the vertical direction is determined based on a head position determining portion 5104 for a carriage HC and the position determining protuberance. In addition, a part of the position determining protuberance of the ink jet head 510 is projected in the direction orienting at a right angle relative to the paper plane of Fig. 3 in such a manner as to allow the head position determining portion 5104 to be covered therewith, whereby the position of the ink jet head 510 is determined by a cutout portion (not shown) of the position determining protuberance and the head position determining portion 5104. A plurality of electrothermal converting elements (each serving as an ink ejection heater) arranged on a silicon base board in the form of a plurality of rows and a plurality of electrical conductors each made of a metallic material such as aluminium or the like to feed electricity to the electrothermal converting elements are formed on a heater board 513 by employing a film forming process. The heater board 513 is electrically connected to a head flexible base board (hereinafter referred to as a head PCB) 5105 including conductors each having a pad disposed at one end thereof for receiving an electrical signal from the ink jet unit while conductors on the heater board 513 side are correspondingly connected to the conductors on the head PCB 5105 side via wire bonding. A plurality of partition walls for separating a plurality of ink flow paths (liquid paths) 515 from each other corresponding to the ink ejection heaters, a common liquid chamber having ink introduced thereinto from an exchangeable ink tank 501 via the ink flow paths 515 so as to feed the ink to the ink flow paths, and a plurality of openings each serving as an ink ejection port are integrally molded of a polysulfone resin or the like to form a grooved ceiling plate 512. Subsequently, the grooved ceiling plate 512 is thrusted against the heater board 513 with the aid of springs (not shown) so that it is sealably secured to the heater board 513 using a sealing agent to form an ink ejecting portion on the ink jet head 510. In this embodiment, to assure that the head base plate 511 can be connected to the exchangeable ink tank 501, a member sealably connected to the grooved ceiling plate 512 and having the ink flow paths 515 formed therein is caused to extend through holes formed through the head PCB 5105 and the head base plate 511 to reach the opposite side of the head base plate 511, and the foregoing member is fixed to the head base plate 511 in the thus formed holes using an adhesive. In addition, a filter 508 is disposed at the left-hand ends of the ink flow paths 515 on the connecting side relative to the exchangeable ink tank 501 in order to prevent dust particles or unnecessary bubbles from entering the ink ejecting portion. The exchangeable ink tank 501 is mechanically connected to the ink jet head 510 with the aid of an engagement guide 505 and a thrusting member 5103 while an ink absorbing member F accommodated adjacent to an ink feeding portion 502 in the ink tank 501 comes in contact with the filter 508 disposed at the foremost end of the ink flow path 515. After completion of the connecting operation, ink can forcibly be fed to the recording head 510 from the exchangeable ink tank 501 by driving a recording head activating recovery pump arranged for the ink jet unit. In this embodiment, while the ink tank 501 is connected to the ink jet head 510 by actuating the thrusting member 5103, a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde in the form of a porous material having a three-dimensional net-shaped structure is accommodated in each of the ink jet head 510 and the exchangeable ink tank 501. Since the ink jet head 501 and the carriage HC are mechanically and electrically connected to each other in the same direction when it is connected to the ink jet head 510, the positions assumed by the pads on the head PCB 5105 and head driving electrodes 5102 are reliably determined. A ring seal 509 is sealably fitted around the left-hand end of the engagement guide 505 in such a manner as to permit the ink feeding portion 502 to be slightly vibratively displaced and has a comparatively large contact area with the right-hand side wall of the exchangeable ink tank 501. In this embodiment, the ring seal 509 is prepared in the form of an elastic ring having a slightly large sectional area. As described above, according to the embodiment of the present invention, after the exchangeable ink tank 501 is firmly connected to the ink jet head 510, the former is thrusted against the latter by actuating the thrusting member 5103, whereby the positions assumed by the carriage HC and the ink jet head 510 can reliably be determined with a simple structure. Since the ink jet head 510 is attached to the carriage HC after the ink jet head 510 and the exchangeable ink tank 501 are simply connected to each other outside of a housing of the ink jet unit, each used empty ink tank 501 can easily be exchanged with a new one. In addition, since the carriage HC and the exchangeable ink tank 501 are electrically connected to each other at the same time, each exchanging operation can be achieved not only for the exchangeable ink tank 501 but also for the ink jet head 501 at a high efficiency. It is acceptable that electrical connection is made for the exchangeable ink tank 501 and the ink jet head 510 by employing a connector connecting process and that the degree of structural freedom is increased in order to more reliably determine the position of the ink jet head 510 and connect the exchangeable ink tank 501 to the ink jet head 510. Next, the structure of an ink cartridge (ink tank) constructed according to the embodiment of the present invention will be described in more detail. Fig. 4 shows by way of schematic sectional view the initial state that an ink tank is divided into two ink chambers a and b each of which is sufficiently filled with ink, and Fig. 5 shows by way of schematic sectional view the state that a quantity of ink capable of being fed from the initial state is storably received in the ink chamber a and a quantity of ink equal to about one third of the volume of the ink chamber b is consumed. In the case that the ink tank is filled with ink in such a manner that the ink chamber b is filled with ink to the volumetric limitative extent in order to maintain a certain negative pressure in the ink tank without any occurrence of ink leakage in the unconnected state, it is preferable that a quantity of ink filled in the ink chamber a is determined to assume a value representing a limit of the ink retaining force of the ink absorbing member or another value smaller than the foregoing value. In this sense, Fig. 4 shows the state that a large part of the ink chamber a is filled with ink within the range defined by the thus determined value. It should be noted that the ink retaining force as mentioned above represents a capability that ink can be retained only in the ink absorbing member after the latter is filled with ink. Referring to Fig. 5 again, the ink received in the compressed ink absorbing member F is retained such that the water head pressure in the ink ejecting portion of the ink jet head, the reduced pressure in the ink chamber b and the capillary power in the compressed ink absorbing member F are kept in the well-balanced state. As ink is fed to the ink jet head side from the ink feeding portion, a quantity of ink received in the ink chamber a is not reduced but the ink in the ink chamber b is increasingly consumed. Specifically, while the inner pressure in the ink tank is kept in the balanced state without any variation of the distribution of ink pressure in the ink chamber a , a quantity of ink corresponding to the quantity of fed ink is displaced to the ink chamber a , and at the same time, a volume of atmospheric air corresponding to the quantity of fed ink is introduced into the ink chamber a through an atmosphere communication portion 503. At this time, air/liquid replacement occurs between atmospheric air and ink through the communication portion between the ink chamber a and the ink chamber b. As ink is fed through the ink feeding portion 502, a part of the meniscus formed on the ink absorbing member F in the ink chamber a and located in the vicinity of the ink chamber b is broken, causing an intensity of pressure in the ink chamber a to be reduced, whereby atmospheric air is introduced into the ink chamber b so as to allow the ink pressure in the ink chamber b to be equalized to the meniscus retaining force of the compressed ink absorbing member F. Thus, an intensity of inner pressure acting on the ink feeding portion 502 is maintained to assume a predetermined value by the capillary force of the ink absorbing member F in the ink chamber a . At this time, a compressing rate of the ink absorbing member at a part of the latter located in the proximity of the ink feeding portion 502 is increased by squeezing the ink flow path 515 of the ink jet head in the ink feeding portion 502 so as to allow the filter 508 to come in close contact with the ink absorbing member F as described above in the aforementioned embodiment. Thus, a larger quantity of ink is distributed at the ink feeding portion 502 so that air/liquid replacement is easily attained along the ink chamber wall 501b. Otherwise, as shown in Fig. 6, a rib 504 is disposed in the ink chamber a between the ink chamber wall 501b and the compressed ink absorbing member F in order to allow atmospheric air to be easily introduced into the ink chamber a through the atmosphere communication portion 503. Fig. 7 shows by way of graph how the inner pressure acting at the ink feeding portion 502 of the exchangeable ink tank 501 constructed according to the embodiment of the present invention varies corresponding to a quantity of fed ink (i.e., a quantity of consumed ink). While the ink tank 501 is held in the initial state, a certain quantity of ink is present also in the ink tank a and a certain intensity of inner pressure is generated in the ink chamber a by the capillary force of the compressed ink absorbing member F. As ink is fed to the ink jet head 510, causing a quantity of ink in the ink chamber a to be reduced, an intensity of inner pressure (negative pressure) generated by the capillary force is gradually increased corresponding to distribution of the compressing rate of the compressed ink absorbing member F (i.e., distribution of pores in the compressed ink absorbing member F). As ink is consumingly fed to the ink jet head 510 further, the ink distribution in the ink tank a is stabilized while ink in the ink chamber b is supplementarily consumed, and subsequently, a substantially constant intensity of inner pressure is maintained by introducing atmospheric air into the ink tank b. When ink in the ink tank b is completely consumed as ink is consumingly fed to the ink jet head 510 further, ink in the ink tank a starts to be consumed again, causing the inner pressure in the ink tank a to vary. When it is detected that an intensity of inner pressure at the ink feeding portion 502 is increased in excess of a predetermined negative value, there arises a necessity for exchanging the used ink tank with a new one or exchanging the used ink tank integrated with the ink jet head with a new one. Fig. 8 is a schematic sectional view of the ink tank constructed according to the embodiment of the present invention, illustratively showing how a compressed ink absorbing member F function as a buffer type ink absorbing member. Specifically, Fig. 8 shows how ink in the ink chamber b flows in the ink chamber a due to expansion of air in the ink chamber b caused as the atmospheric pressure is decreased or the atmospheric air temperature is elevated from the state as shown in Fig. 5. With respect to the relationship between a quantity of ink absorbed in the compressed ink absorbing member F and each ink chamber, it is acceptable from the viewpoint of preventing ink from leaking from the ink tank when the atmospheric pressure is decreased or the atmospheric temperature varies as mentioned above that a maximum quantity of ink absorption in the ink chamber a is determined in consideration of a quantity of ink flowing from the ink chamber b under worst conditions and a quantity of ink storably received in the ink chamber a when ink is fed from the ink chamber b and that the ink chamber a has at least a large volumetric capacity enough to accommodate the compressed ink absorbing member F therein. Fig. 9 is a graph which shows the relationship between a volume of initial hollow space of the ink chamber b prior to decreasing of the atmospheric pressure and a quantity of ink flowing outside of the hollow space of the ink tank when the atmospheric pressure of the ink chamber a is decreased to a level of 0.7 at. In addition, the case that a condition of maximum decreasing of the atmospheric pressure is shown by a one-dotted chain line in Fig. 9. When a quantity of ink flowing from the ink chamber b is estimated, e.g., in the case that a condition of maximum decreasing of the atmospheric pressure is set to 0.7 at, a maximum quantity of ink flowing from the ink chamber b corresponds to the case that ink remains in the ink chamber b by a quantity equal to 30 % of a volumetric capacity VB of the ink chamber b. Thus, when it is assumed that ink remaining below the lower end of the ink chamber wall is absorbed in the compressed ink absorbing member accommodated in the ink chamber a , it may be considered that all the ink remaining in the ink chamber b (equal to 30 % of the volumetric capacity VB) leaks from the latter. In the case that a worst condition of the atmospheric pressure is set to 0.5 at, ink flows from the ink chamber b by a quantity equal to 50 % of the volume of the ink chamber b. The volume of air in the ink chamber b expanded under the decreased pressure is enlarged as a quantity of ink remaining in the ink chamber b is reduced more and more but it does not flow from the ink chamber b in excess of a quantity of ink in the ink chamber b. Therefore, in the case that it is presumed that a condition of maximum decreasing of the atmospheric pressure is set to 0.7 at, when a quantity of ink remaining in the ink chamber b is reduced to a level of 30 % or more, a quantity of remaining ink becomes smaller than a quantity of expansion of the atmospheric air, resulting in a quantity of ink flowing to the ink chamber a being reduced. Thus, a maximum quantity of leaked ink is represented by 30 % of the volumetric capacity of the ink chamber b (corresponding to 50 % under a condition of 0.5 at). The ink used for practicing this embodiment has the following composition. COMPOSITION pigment 4 parts glycerol 7.5 parts thioglycol 7.5 parts urea 7.5 parts pure water 73.5 parts This kind of ink is ink preferably employable for printing characters each having a high quality on a so-called plain paper such as a copying paper, a bond paper or the like. Generally, it is mentioned that ink employable for performing an ink jet type printing operation can be impregnated in a paper at a higher speed as a value of η/(γ cos ) is reduced more and more. Here, η designates a viscosity of the ink, γ designates a surface tension of the ink, and  designates a contact angle defined between the ink and the paper. Generally, when the contact angle is reduced and the ink is impregnated in the paper at a high speed, the ink is caused to ooze along irregularly distributed fibers on the opposite surfaces of the paper, resulting in a quality of printed image being degraded. One of measures to be taken for improving a quality of printed image is to increase a rate of water in the ink (representing a high value of γ and a high value of ). In this case, however, a property of impregnation of the ink in the paper is degraded. The ink having the above-noted composition exhibits a high surface tension ranging from 40 to 50 dyne/cm. Thus, a quality of printed image can be improved with this ink by degrading the property of ink in a paper in consideration of a good balance to be maintained in association with a fixing property while preventing the ink from being spread over the opposite surfaces of the paper, causing the ink to ooze along irregularly distributed fibers. The inventors conducted a series of reduced pressure tests using ink of the foregoing kind and a polyurethane foamed block accommodated in one of the aforementioned ink tanks as an ink absorbing member, and it was found as a result derived from the tests that some of the ink tanks had a problem that ink leaked outside of each ink tank because a quality of fabrication of these ink tanks fluctuated from tank to tank. However, an occurrence of ink leakage could be prevented by using a melamine foamed block as an ink absorbing member. Specifically, it was found as a result derived from examinations conducted by the inventors that the problem of ink leakage could be solved by improving not only a volumetric property of an ink buffer chamber but also a hydrophilic property of the ink absorbing member accommodated in the ink tank, and moreover, using a melamine foamed block having a hydrophilic property higher than that of the conventional polyurethane foamed block. It should be noted that the melamine foamed block is a porous member having a three-dimensional net-shaped structure which is one of foamed blocks each molded of a condensate composed of a compound having an amino group and formaldehyde. Fig. 10 to Fig. 12 are schematic ink absorbing memberal views each of which shows by way of comparative example the structure of an ink tank constructed according to the embodiment of the present invention wherein a polyurethane foamed block F' is used as an ink absorbing member but a malfunction of ink leakage occurs with the ink tank, respectively. Fig. 10 shows an initial state of the ink tank, and Fig. 11 shows the state that ink capable of being fed to an ink chamber a from the initial state and a quantity of ink equal to about one fifth of a volume of an ink chamber b are consumed. Fig. 12 shows the state that ink in the ink tank b is squeezed to the ink chamber a from the state shown in Fig. 11 due to reduction of the atmospheric pressure and elevation of the atmospheric temperature. A large part of the ink is absorbed in the ink absorbing member (polyurethane foamed block) F' having ink preliminarily impregnated therein but the other part of ink is not absorbed in the ink absorbing member (polyurethane foamed block) F' but flows along a gap between an ink tank wall 501a and the ink absorbing member (polyurethane foamed block) F' as well as a gap between an ink chamber wall 501b and the ink absorbing member (polyurethane foamed block) F' until it leaks outside of the ink tank 501 through an atmospheric air communication portion 503. The foregoing problem of ink leakage is attributable to the fact that since the water absorbing ink absorbing member F' composed of a polyurethane foamed block exhibits a water repelling property also to ink, the surface state of a part of the ink absorbing member F' having ink once absorbed therein varies, enabling a certain quantity of ink to be absorbed therein again, but another part of the water absorbing ink absorbing member F' having no ink absorbed therein unchangeably maintains the water repelling property, resulting in an ink absorbing property of the ink absorbing member F' being degraded. On the other hand, Fig. 13 shows how ink flows in the ink tank 501 at the time of a reduced atmospheric pressure in the case that a melamine foamed block F is used as an ink absorbing member. In contrast with the polyurethane foamed block, the melamine foamed block F has an excellent hydrophilic property. For this reason, the ink flows from the ink chamber b is quickly absorbed in any part of the melamine foamed block F having no ink preliminarily absorbed therein. As is apparent from the drawing, ink absorption is gradually achieved from the communication portion between the ink chamber a and the ink chamber b toward the atmospheric air communication portion 503. Thus, the ink chamber a can fully be utilized as an ink buffer chamber. Utilization of the ink tank 501 is finally terminated when the ink absorbed in the ink absorbing member accommodated in the ink chamber a is completely consumed. Subsequently, when the polyurethane foamed block and the melamine foamed block are compared with each other, a difference is recognized in respect of a quantity of remaining ink (i.e., a quantity of ink incapable of being used) therebetween. This is attributable to the fact that since no film is formed on the melamine foamed block after completion of a molding operation, there does not arise a malfunction that a certain quantity of ink remains in the ink absorbing member due to the formation of a film or the presence of a residue of the foamed block like the polyurethane foamed block after ink is consumed, resulting in the ink being fully consumed at a high efficiency. In practical use, the melamine foamed block F having a pore size ranging from 100 µm to 800 µm was accommodated in the space of the ink tank 501 defined between the inner wall surface of the ink chamber wall 501b and the ink feeding portion 502 in the compressed state that the melamine foamed block F was compressed to an extent represented by a numeral of 1.1. A series of reduced pressure tests were conducted by the inventors under a condition that the ink tank having the melamine foamed block F accommodated therein was mounted on an ink jet unit. It was confirmed as a result derived from the tests that the ink tank advantageously employable for the ink jet unit could be realized without any occurrence of ink leakage while maintaining a high quality of printed image. Fig. 14 and Fig. 15 are schematic ink absorbing memberal views each of which shows an ink tank constructed according to an embodiment modified from the embodiment of the present invention, respectively. In each of these embodiments, two ink chambers c and d are additionally arranged in the ink tank while making communication with an ink chamber b. With this construction, ink is consumed in accordance with the order of the ink chamber b, the ink chamber c and the ink chamber d as seen from the right-hand side of each drawing. In these embodiments, the reason why the ink tank is divided into four ink chambers consists in preventing ink from leaking from the ink tank under the reduced pressure atmosphere when the atmospheric temperature varies. For example, in the case that atmospheric air in the ink chamber b and the ink tank chamber c is expanded while the state as shown in Fig. 15 is maintained, a quantity of expanded atmospheric air in the ink chamber b is released through the atmospheric air communicating portion 503 via the ink chamber a , and a quantity of expanded atmospheric air in the ink chamber c is released by flowing ink in the ink chamber b and the ink chamber a from the ink chamber c. In other words, the ink chamber a exhibits a function of serving as a buffer chamber, and therefore, it is acceptable that an ink retaining capacity of the ink absorbing capacity F accommodated in the ink chamber a in the compressed state is determined in consideration of a quantity of ink which leaks outside of the ink chamber a . Also in this embodiment, it is obvious that an effect derived from the buffer chamber is maximized by using the melamine foamed block F for an ink absorbing member to be accommodated in the ink chamber a . While the embodiment of the present invention has been described above with respect to a monochromatic ink jet unit including a single ink jet head, it can equally be applied to a color ink jet unit including a plurality of ink jet heads each capable of ejecting an ink having a different color, e.g., four ink jet heads adapted to eject four kinds of inks having colors black, cyan, magenta and yellow. In addition, it can equally be applied to a single ink jet head which is designed to eject plural kinds of colors therefrom. In this case, it is recommendable that an exchangeable ink tank is additionally equipped with means for limitatively determining the position where the exchangeable ink tank is connected to the color ink jet unit as well as the direction of connecting the exchangeable ink tank to the color ink jet unit. Further, while the embodiment of the present invention has been described above with respect to the case that an ink tank can be exchanged with another one, it can equally be applied to an ink jet unit of the type including an ink jet head integrated with an ink tank having a predetermined quantity of ink filled therein. (Modified Embodiment of the Embodiment) Fig. 16 is a schematic ink absorbing memberal view of a head cartridge constructed according to an embodiment modified from the embodiment of the present invention, particularly showing the function of an ink tank integrated with an ink jet head. An exchangeable ink tank 501 is divided into four ink chambers, i.e., an ink chamber a , an ink chamber b, an ink chamber c and an ink chamber d which are communicated with each other through apertures formed on the bottom thereof. An ink feeding portion 502 is disposed in the ink chamber a , an ink absorbing member F of which capillary force is adequately adjusted is accommodated in the ink chamber a and the communicating portion extending across the ink chambers b, c and d in the compressed state, and a buffer type ink absorbing member F B serving to prevent an occurrence of ink leakage is accommodated in the ink chamber d having an atmospheric air communicating portion 503 formed therethrough. In other words, the head carriage is constructed in the form of an improved type ink cartridge. The state of an ink tank 501 shown in Fig. 16 represents the operative state of the head cartridge that a quantity of ink equal to about a half of the volumetric capacity of the ink chamber c is consumed from the initial state that ink is sufficiently filled in the ink chamber a , the ink chamber b and the ink chamber c. When ink in the ink chamber c disappears as ink is consumed further, ink in the ink chamber b starts to be fed from the latter as shown in Fig. 17. Thereafter, when the ink in the ink chamber b disappears as ink is consumed further from the state shown in Fig. 17, ink retained in an ink absorbing member F accommodated in the ink chamber a starts to be fed from the latter. Subsequently, when the ink in the ink chamber a substantially disappears, the ink tank 501 is exchanged with a new one. Fig. 18 is a schematic fragmentary enlarged ink absorbing memberal view of a head cartridge constructed according to an embodiment modified from the embodiment of the present invention, particularly explaining a principle of ink feeding and generation of an inner pressure in an ink tank. Referring to Fig. 18, ink in the left-hand ink chamber is substantially consumed. At this time, since the left-hand ink chamber is communicated with an atmospheric air communication portion 503 by the function of a communicating portion between adjacent ink chambers, an atmospheric pressure is introduced into the left-hand ink chamber through the atmosphere air communicating portion 503. As ink is fed from the ink feeding portion 502 to the ink jet head side, ink flows from an ink chamber located adjacent to the left-hand ink chamber via the ink absorbing member F of which capillary force is intensified by the compression given by the communicating portion between adjacent ink chambers. As ink is consumed in each ink chamber, an intensity of pressure in the ink chamber is correspondingly reduced, whereby a meniscus formed over the ink absorbing member F compressed between adjacent ink chambers is partially broken, causing an atmospheric air to be introduced into the ink chamber in such a manner as to allow the reduced pressure in the ink chamber to be held in the balanced state relative to the meniscus retaining force of the compressed ink absorbing member. Thus, the inner pressure at the ink feeding portion 502 is maintained to assume a predetermined value by the capillary force of the compressed ink absorbing member located at the communicating portion between the adjacent ink chambers. Fig. 19 is a graph which shows how the inner pressure at the ink feeding portion of the exchangeable ink tank 501 constructed according to the modified embodiment of the present invention varies corresponding to a quantity of fed ink (i.e., a quantity of consumed ink). Although the inner pressure is generated by the capillary force given by the buffer type ink absorbing member F B or the ink absorbing member F, a certain intensity of inner pressure is generated by the capillary force given by a part of the compressed ink absorbing member (compressed part) located at the communicating portion between the ink chamber d and the ink chamber c as ink is fed from the ink feeding portion 502. As long as ink is fed from the ink chamber c, a substantially constant intensity of inner pressure is maintained. As ink is consumed further, ink in the ink chamber b starts to be fed, and the inner pressure at the ink feeding portion slightly varies every time the working ink tank is shifted to a subsequent one. It is considered that this is associated with the facts that while ink is continuously fed from the ink feeding portion 502, the inner pressure is measured and that the state of a reduced intensity of inner pressure in each of the ink chamber c and b temporarily appears. However, it has been confirmed by the inventors that no serious problem appears in respect to functional properties such as recording properties of a recording head or the like. When ink in the ink chamber b is stably consumed, the inner pressure at the ink feeding portion 502 is stabilized again. When the ink in the ink tank b is completely consumed, ink in the next ink chamber a starts to be fed (consumed) from the ink feeding portion 502. The inventors conducted a variety of examinations, and as a result derived from the examinations, they confirmed that a good printing operation could be performed without any particular problem during the period of stable ink feeding as shown in Fig. 19. Fig. 20 is a schematic ink absorbing memberal view of a head cartridge constructed according to another embodiment modified from the embodiment of the present invention, particularly showing how a buffer type ink absorbing member function. Specifically, Fig. 20 shows how ink in the ink chamber c overflows from the latter due to expansion of the air in the ink chamber c induced by decrease of the atmospheric pressure or elevation of the atmospheric temperature. In this embodiment, the ink overflowed in the ink chamber d is retained in the buffer type ink absorbing member F B . In view of the foregoing fact, it is acceptable that a quantity of ink to be absorbed in the buffer type ink absorbing member F B is determined in consideration of the fact that ink leaks from the ink chamber c by a quantity equal to at largest 30 % of the volumetric capacity of the ink chamber c in the case that the atmospheric air has a reduced pressure of 0.7 at. When the atmospheric pressure is restored to the original level (corresponding to 1 at) before it is reduced, the ink overflowed in the ink chamber d and retained in the buffer type ink absorbing member F B returns to the ink tank c again. The aforementioned phenomenon likewise equally appears also in the case that the temperature of the ink tank varies. For example, when the temperature of the ink tank is elevated by about 50 °C, a quantity of ink leaked from the ink chamber c is smaller than that at the time of pressure reduction. Also in this case, it is considered that it is acceptable that an ink buffer is designed in consideration of a maximum quantity of leaked ink. In this connection, the inventors conducted a series of reduced pressure tests, and as a result derived from the reduced pressure tests, it was confirmed by them that a problem of ink leakage arose with some ink tanks each having a polyurethane foamed block used for a buffer type ink absorbing member but the same problem of ink leakage as mentioned above did not arise with an ink tank having a melamine foamed block having an excellent hydrophilic property used as a buffer type ink absorbing member. As described above, according to the embodiment of the present invention, a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde is used as a base material for an ink tank cartridge including an ink chamber having an ink feeding portion disposed therein and one or a plurality of ink chambers communicated with the first-mentioned ink chamber having an ink absorbing member accommodated therein of which capillary force is adequately adjusted, and the ink absorbing member accommodated in the first-mentioned ink chamber has a porous three-dimensional net-shaped structure and ink is storably filled in each of the last-mentioned ink tanks. With this construction, any ink leakage does not occur with the ink tank cartridge irrespective of variation of the working environment of the ink jet unit not only when a printing operation is performed but also when no printing operation is performed with the ink jet unit. Consequently, the ink tank cartridge having a high ink consumption efficiency and an excellent quality of printed image can be realized according to the present invention. Fig. 21 is a perspective view of an ink jet printing apparatus adapted to perform a printing operation using a head cartridge constructed according to each of the embodiments and the modified embodiments of the present invention as mentioned above. In the drawing reference numeral 109 designates a head cartridge including an ink tank and a printing head integrated with each other, and reference numeral 111 designates a carriage having the head cartridge 109 mounted thereon to perform a scanning operation in the S arrow-marked direction. Reference numeral 113 designates a hook for securing the head cartridge 109 to the carriage 111, and reference numeral 115 designates a lever for actuating the hook 113. A plurality of markers 117 are impressed on the lever 115 for enabling the position where a printing operation is performed with the printing head at present and the position where the lever 115 has been actuated to be visually read by a user based on a plurality of calibrations recessed on a cover (not shown) for the ink jet printing apparatus. Reference numeral 119 designates a support plate for supporting electrical connecting portions to be electrically connected to the head cartridge 109, and reference numeral 121 designates a flexible cable for electrically connecting the electrical connecting portions to a main controlling ink absorbing member for the ink jet recording apparatus. Reference numeral 123 designates a guide shaft for guiding the reciprocable displacement of the carriage 111 in the S arrow-marked direction. The guide shaft 123 is inserted through a bearing 125 of the carriage 111. Reference numeral 127 designates an endless timing belt fixedly secured to the carriage 111 for transmitting a power required for reciprocably displacing the carriage 111 in the S arrow-marked direction. The timing belt 127 is spanned between a pair of pulleys 129A and 129B disposed on the opposite sides of the ink jet printing apparatus. A certain intensity of driving power is transmitted from a carriage motor 131 to the right-hand pulley 129B via a power transmitting mechanism including gears and others. Reference numeral 133 designates a conveyance roller for conveying a printing medium such as a paper or the like while restrictively defining a printing plane of the printing medium. The conveyance roller 133 is rotationally driven by a conveyance motor 135. Reference numeral 137 designates a paper pan for bringing the printing medium to the printing position from the paper feeding tray 104 side, and reference numeral 139 designates a feed roller disposed at the intermediate position located on a feeding path for the printing medium for conveying the printing paper while thrusting the latter against the conveyance rollers 133. Reference numeral 134 designates a platen located opposite to an ink ejecting port of the head cartridge 109 for restrictively defining the printing plane of the printing medium, and reference numeral 141 designates a paper discharging roller disposed at the position located downstream of the printing position as seen in the printing medium conveying direction for discharging the printing medium toward a paper discharging port (not shown). Reference numeral 142 designates a pulley disposed opposite to the paper discharging roller 141 for generating a conveying power required for conveying the printing medium in cooperation with the paper discharging roller 141 while thrusting the latter via the printing medium, and reference numeral 143 designates a releasing lever for releasing the feed roller 139, a retaining plate 145 and the pulley 142 from the thrusted state. Reference numeral 145 designates a retaining plate disposed for suppressively preventing the printing medium from being floated up at the position located in the printing position. In the shown case, a printing head adapted to perform a printing operation by ejecting ink is employed for the ink jet printing apparatus. Thus, a distance between the ink ejecting port forming plane of the printing head and the printing plane of the printing medium is comparatively small, and moreover, since the foregoing distance should strictly be controlled in order to preventing the printing medium from coming in contact with the ink ejecting port forming plane, it is advantageously acceptable that the retaining plate 145 is disposed in the above-described manner. Reference numeral 147 designates a series of calibrations impressed on the retaining plate 145, and reference numeral 149 designates a marker formed on the carriage 111 to correspond to one of the calibrations 147. with this construction, the position where each printing operation is performed with the printing head and the position where the printing head is mounted for the ink jet printing apparatus can visually be read by a user with the aid of the calibrations 147 and the marker 149. Reference numeral 151 designates a cap disposed opposite to the ink ejecting port forming plane of the printing head. The cap 151 is molded of an elastic material such as a rubber or the like, and it is supported in such a manner as to enable it to be brought in contact with the ink ejecting port on the printing head and then released from the contact state relative to the printing head. The cap 151 is used for the purpose of protecting the printing head from damage or injury Or allowing the printing head to be subjected to suction recovering treatment when no printing operation is performed with the printing head. The suction recovering treatment represents a treatment to be executed in such a manner that the cap 151 is located opposite to the ink ejecting port forming plane of the printing head and ink is then ejected from the ink ejecting port by activating the energy generating element disposed inside of the ink ejecting port for generating energy to be utilized for the purpose of ink ejection whereby a factor of causing incorrect ink ejection due to the presence of bubbles, dust particles or ink having an increased viscosity unsuitably employable for each printing operation is eliminated. In addition, the suction recovering treatment represents another treatment to be executed in such a manner that a factor of causing incorrect ink ejection is eliminated by forcibly ejecting ink from the ink ejecting port while the ink ejecting plane of the printing head is covered with the cap 151. Reference numeral 153 designates a pump for allowing a suction force effective for forcibly ejecting ink from the ink ejecting port to be applied to the printing head, and moreover, sucking the extra ink received in the cap 151 for executing suction recovering treatment subsequent to the forcible ink ejection or suction recovering treatment subsequent to preliminary ink ejection. Reference numeral 155 designates a waste ink tank in which waste ink sucked by the pump 153 is storably received, and reference numeral 157 designates a tube for making communication between the pump 153 and the waste ink tank 155. Reference numeral 159 designates a blade for wiping the ink ejecting port forming plate of the printing head. The blade 159 is supported in such a manner as to be displaced to the position where a wiping operation is performed in the course of displacement of the printing head while the blade 159 is projected toward the printing head side as well as the position where the blade 159 is retracted away from the ink ejecting port forming plane of the printing head without any contact with the latter. Reference numeral 161 designates a motor, and reference numeral 163 designates a cam assembly for driving the pump 153 and displacing the cap 151 and the blade 159 with the driving power transmitted from the motor 161.

Claims: An ink tank connectable to an ink jet head of an ink jet printing apparatus, said ink tank comprising: a first chamber having a negative pressure generation member accommodated therein and including a liquid supplying portion for supplying liquid to the ink jet head and an atmospheric air communicating portion communicating with atmospheric air; and a second chamber communicating with said first chamber through a communication portion disposed apart from said atmospheric air communicating portion, said second chamber retaining liquid for supply to said first chamber and being substantially sealed except at said communication portion, wherein said negative pressure generation member is a porous member having a three-dimensional net-shaped structure and is molded of a condensate composed of a compound having an amino group and a formaldehyde. An ink tank as claimed in claim 1, wherein said ink tank is separable from a printing head so as to enable it be exchanged another one. A head cartridge, comprising: an ink tank including a first chamber having a negative pressure generation member accommodated therein and including a liquid supplying portion for supplying liquid to an ink jet printing head and an atmospheric air communicating portion communicating with atmospheric air, and a second chamber communicating with said first chamber through a communication portion disposed apart from said atmospheric air communicating portion, said second chamber retaining liquid for supply to said first chamber and being substantially sealed except at said communication portion, wherein said negative pressure generation member is a porous member having a three-dimensional net-shaped structure and is molded of a condensate composed of a compound having an amino group and a formaldehyde; and said printing head, said printing head allowing ink to be fed from said ink tank an then ejecting the fed ink therefrom. A head cartridge as claimed in claim 3, wherein said printing head includes an energy generating element for generating energy to be utilized for the purpose of ink ejection. A head cartridge as claimed in claim 4, wherein said printing head includes an electrothermal converting element for generating thermal energy required for generating a bubble in said ink, said electrothermal converting element serving as said energy generating element. An ink jet printing apparatus, comprising: a head cartridge including an ink tank including a first chamber having a negative pressure generation member accommodated therein and including a liquid supplying portion for supplying liquid to an ink jet printing head and an atmospheric air communicating portion communicating with atmospheric air, and a second chamber communicating with said first chamber through a communication portion disposed apart from said atmospheric air communicating portion, said second chamber retaining liquid for supply to said first chamber and being substantially sealed except at said communication portion, wherein said negative pressure generation member is a porous member having a three-dimensional net-shaped structure and is molded of a condensate composed of a compound having an amino group and a formaldehyde, and said printing head, said printing head allowing ink to be fed from said ink tank and then ejecting the fed ink therefrom, wherein said printing head includes an energy generating element for generating energy to be utilized for the purpose of ink ejection, said printing head includes an electrothermal converting element for generating thermal energy required for generating a bubble in said ink, said electrothermal converting element serving as said energy generating element, and said printing head is detachably mounted on said ink jet printing apparatus.

Inventors: HIGUMA MASAHIKO, ISHINAGA HIROYUKI, KAWAI JUN, MASUDA KAZUAKI, OHTA TOKUYA, OSADA TORACHIKA, SAITO TAKASHI, SATO YOHEI, SUGITANI HIROSHI, TANEYA YOICHI, HIGUMA, MASAHIKO, ISHINAGA, HIROYUKI, KAWAI, JUN, MASUDA, KAZUAKI, OHTA, TOKUYA, OSADA, TORACHIKA, SAITO, TAKASHI, SATO, YOHEI, SUGITANI, HIROSHI, TANEYA, YOICHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: B41J2
IPC codes: B41J2